Present embodiments relate generally to a gas turbine engine. More specifically, the present embodiments relate, but are not limited to, reducing leakage at a in a low pressure turbine section of a gas turbine engine.
A typical gas turbine engine generally possesses a forward end and an aft end with its several core or propulsion components positioned axially therebetween. An air inlet or intake is located at a forward end of the engine. Moving toward the aft end, in order, the intake is followed by a fan, a compressor, a combustion chamber, and a turbine. It will be readily apparent from those skilled in the art that additional components may also be included in the engine, such as, for example, low-pressure and high-pressure compressors, and low-pressure and high-pressure turbines. This, however, is not an exhaustive list.
The compressor and turbine generally include rows of airfoils that are stacked axially in stages. Each stage includes a row of circumferentially spaced stator vanes and a row of rotor blades which rotate about a center shaft or axis of the turbine engine. A multi-stage low pressure turbine follows the multi-stage high pressure turbine and is typically joined by a second shaft to a fan disposed upstream from the compressor in a typical turbo fan aircraft engine configuration for powering an aircraft in flight.
The stator is formed by a plurality of nozzle segments which are abutted at circumferential ends to form a complete ring about the axis of the gas turbine engine. Each nozzle segment may comprise a single vane, commonly referred to as a singlet. Alternatively, a nozzle segment may have two vanes per segment, which are generally referred to as doublets. In a third embodiment, additional numbers of vanes may be disposed on a single segment. In these embodiments, the vanes extend between an inner band and an outer band.
A typical gas turbine engine utilizes a high pressure turbine and low pressure turbine to maximize extraction of energy from high temperature combustion gas. The turbine section typically has an internal shaft axially disposed along a center longitudinal axis of the engine. The blades are circumferentially distributed on a rotor causing rotation of the internal shaft. The internal shaft is connected to the rotor and the air compressor, such that the turbine provides a rotational input to the air compressor to drive the compressor blades. This powers the compressor during operation and subsequently drives the turbine. As the combustion gas flows downstream through the turbine stages, energy is extracted therefrom and the pressure of the combustion gas is reduced.
In operation, air is pressurized in a compressor and mixed with fuel in a combustor for generating hot combustion gases which flow downstream through turbine stages. These turbine stages extract energy from the combustion gases. A high pressure turbine first receives the hot combustion gases from the combustor and includes a stator nozzle assembly directing the combustion gases downstream through a row of high pressure turbine rotor blades extending radially outwardly from a supporting rotor disk. The stator nozzles turn the hot combustion gas in a manner to maximize extraction at the adjacent downstream turbine blades. In a two stage turbine, a second stage stator nozzle assembly is positioned downstream of the first stage blades followed in turn by a row of second stage rotor blades extending radially outwardly from a second supporting rotor disk. The turbine converts the combustion gas energy to mechanical energy.
During such operation of the gas turbine engine, it is desirable to minimize thermally induced deformation of the outer casing through the turbine section of the engine. This is accomplished, according to some embodiments, by isolating the outer casing from heat produced by the hot combustion gases flowing through the turbine. Turbine shrouds are connected to the engine casing to provide an outer boundary flow for the combustion gas limiting high temperature combustion gas from adversely affecting the casing. The shroud extends circumferentially to form a ring shape and may be formed of a plurality of circumferentially extending shroud segments. However, as combustion gas moves radially outward with rotation of the turbine blades, the combustion gas can pass through axial seams between the adjacent shroud segments. This is not optimal and results in energy losses.
It would be desirable to overcome these and other deficiencies with turbine sections of gas turbine engines. More specifically it would be desirable to provide a restriction in at least a radial direction to flow of combustion gas between shroud segments.